Why is there a direct connection with vegetarianism and mental health..?

I’m doing a project on Mental Health, and there seems to be some correlation between Vegetarians and Mental health , What I need to know is if there is some missing nutrients or the absent of amino acids and the reflect those have or the brain……Thanks
I posted this question in Vegetarian category it didn’t go over so well, boy they are a loose bunch, kind of accentuates my question..

vitamin B12.
it’s found in meat, milk, and eggs, but particularly meat.
it has direct impact on the brain, especially the part that causes you to hallucinate, have delusions, and illusions.
also, the amino acid triptophan is said to have direct effect on certain mental disorders. animals that did not get enough of this amino acid in their diets tended to express self-harming behaviors. people who do not get enough triptophan in their diets were said to commonly express these signs of mental stress:
depression
anxiety
irritability
impatience
impulsiveness
inability to concentrate
weight gain or unexplained weight loss
slow growth in children
overeating and/or carbohydrate cravings
poor dream recall
and insomnia.
triptophan is commonly found in meat products such as chicken, turkey, tuna fish, shrimp, and salmon.

i’m sure there are many more vitamins and such that effect neurotransmitters and other like aspects in the brain, but i haven’t studied this or anything so i really don’t know. sorry.

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